Development of immobilized reagents, catalysts, and scavengers for application in various chemical protocols continues to be important. Since the introduction of polystyrene immobilized resins, a variety of immobilization agents have been found, such as silica, fluorous, monolith, and polymers generated from ring-opening metathesis polymerization (“ROMP”). Investigations into these types of agents have resulted in surface functionalization of nanoparticles via polymer grafting. This technique provides a method for the preparation of particle-polymeric hybrid materials. Such hybrid materials combine the physical properties of the inorganic shell (e.g., particle size, pore and shape) with the tunable properties of the grafted organic polymer. Grafted-hybrid materials, such as silica-polymer hybrids, may be important and useful as heterogeneous supported catalysts, which can be used in the automotive, electronic, and consumer industries. As such, surface-initiated ROMP can be used as an effective method for the grafting of organic-polymers from inorganic nano-particles, carbon nano-tubes, metal surfaces, and resins.
Also, current asymmetric homogeneous catalysts are difficult to use in large-scale runs, as they are not reusable, and can contaminate the desired products. To address these limitations, the immobilization of these key metal catalysts could be utilized as one method to resolve these limitations, while opening up their key utilization in continuous flow through processing has been the immobilization of such catalysts, specifically through immobilization of the corresponding ligands to anchor the metals to the support. Strong binding of the catalyst to the support prevents metal leaching into product, whilst improving turnover number. In addition, it has been reported that metal catalysts prone to dimerization (e.g. Ruthenium) and hence deactivated can be prevented via immobilization, extending the catalyst life more than just the added cause of recycling.
Though limited, a variety of platforms have been developed for the immobilization of metal catalyst/ligand systems, including fluorous tagged enantiopure phosphine-phosphite ligands, soluble PEG-monophosphite ligands, phosphoramidites, phosphines, silica-grafted phosphite and phosphine ligands, polystyrene-supported phosphine ligands, and other ligand systems. Despite these advancements, difficulties in isolation, recyclability and the inherent low load levels of current immobilized ligands/metal catalysts hampers their application in various chemical synthesis protocols. Thus, these key properties must be optimized in order to improve performance in parallel synthetic methods. Moreover, enhancement in load is absolutely critical for expansion of immobilized ligand/metal catalysts in green, efficient parallel automated technologies.
Therefore, there remains a need in the art to improve immobilization of agents that can be used in catalytic protocols.